1. Field of the Invention
The present invention relates to an image reading apparatus suitable as being applied to a scanner, a copier, a facsimile apparatus, a digital multi-function apparatus or such.
2. Description of the Related Art
As typical reading systems of a color image reading apparatus, a light source switching system and a color sensor system may be cited.
The light source switching system is such that light sources of three colors, i.e., R (red), G (green) and B (blue), and a single line sensor are provided. For each scanning line of the line sensor, the R, G and B light sources are switched. As a result, each line image data of RGB can be obtained.
The color sensor system is such that, R, G and B three sorts (pierces) of color line sensors and a white light source are provided. R, G and B are read simultaneously for one scanning line on each line sensor (the same time for the respective line sensors).
In the light source switching system, the single line sensor is shared for the line image data in the RGB respective colors in a time sharing manner. Accordingly, a reading speed is relatively slow. At the same time, since only a single channel of image data serially output by the single line sensor is processed, the circuit configuration can be simplified (see Japanese Laid-open Patent Applications Nos. 2003-319150 and 10-136154). Throughout the specification, ‘serially outputting’ means that image data is output in line units for each color in sequence.
On the other hand, in the color sensor system, serial image data is output in parallel from respective channels of the three single color line sensors for R, G and B. Accordingly, the reading speed can be made relatively higher. At the same time, only a single image processing circuit is not sufficient, and three image processing circuits are required for simultaneously processing the serial image data from the respective channels in parallel. Accordingly, the costs may rise.